Declaring parameters after a starred parameter results in keyword-only arguments. If these arguments are not supplied a default value, then calls to the function will raise an error if the keyword argument is not supplied, as seen above.

Notice the use of += which is a shortcut operator, so instead of saying x = x + y, you can say x += y.

If you want to have keyword-only arguments but have no need for a starred parameter, then simply use an empty star without using any name such as def total(initial=5, *, extra_number).